Your guide to the Cannabis Seedling Stage

Growing

The cannabis seedling stage is the time when your weed plants are at their most tender and vulnerable. It seems like a long journey before they will be harvest-ready plants. Learning how to protect and care for your seedlings is essential – and luckily it isn’t that difficult – so read our guide to taking care of your baby plants which contains all you need to know.

Germination

When your cannabis seeds burst into life and sprout two tiny leaves and send roots into the soil (or whatever germinating medium you are using), they are known as seedlings. Keep an eye on the seeds to check that the soil does not dry out and after a few weeks, you should see signs that the seeds are splitting, and the tendril emerging. This will head downwards into the soil and eventually form the taproot. This tiny white spike is the first sign of life of a new cannabis plant. Nothing is more rewarding than seeing the evidence that the seeds you have carefully selected have woken from their dormancy and are embarked on a new life stage which will end in rich rewards for you!

Meanwhile, the husk of the seeds splits into two and provides energy to fuel the growth of the seedlings. You should soon see two leaves unfurling. These first leaves are known as ‘sucker leaves’ or cotyledons and are smooth and round. Don’t worry if they look nothing like cannabis leaves; this is normal. All plants begin by producing sucker leaves. Their role is to support photosynthesis and collect enough energy for the plant to grow. The next pairs of leaves should be more cannabis-like in appearance, although it will take a while before the seedling is mature enough to produce genuine cannabis leaves.

How to protect your seedlings?

Cannabis seedlings, as is the case for all young plants, are extremely vulnerable to many types of danger. Birds may eat them, they could be damaged by frost, dry out from lack of water, or ravaged by pests. Some may die from unknown causes, and this is common, but you need to do all you can to protect them until they grow into strong young plants.

They need a shelter with some sort of transparent, plastic shield. If growing outside, you could place them under plastic bottles, cut in half with extra slots cut into the sides to promote airflow. These protect vulnerable seedlings from excess rain as well as predators. You can buy ready-made cloches at garden centres.

When germinating cannabis seeds indoors, just make sure that they are in a safe place, well away from any children and pets. Nothing is more annoying than finding a cat sitting on a tray of sprouting seedlings!

Irrigation

One of the most common causes of death in seedlings is root rot caused by overwatering and insufficient oxygen in the soil or substrate. This is more likely to happen with beginner growers who have no gardening experience.

Cannabis plants at the early stages of their life have very few needs; they do not need too much water. If water swamps the delicate root system, it will quickly cease to grow and will die in the space of a few days. One way of preventing this is to use small pots for seedlings as the soil dries much more quickly than in larger containers.

Weed seedlings should be watered carefully. Do not pour a watering can of water all over them, for example, or use a hosepipe, unless you want to drown them or wash them away. Use small amounts of water and use a small jug or sprayer to give it gradually.

Don’t give so much water that it puddles, but equally do not allow the soil or substrate to dry out.

If you have forgotten to water your plants for a few days you may find that the soil has dried out so much that the water runs straight out the pot. If this happens – which it shouldn’t as you need to check your seedlings a couple of times each day! – add water ten minutes later, and then twenty minutes later, and so on. This enables the soil to absorb the water gradually.

Which water is best for cannabis seedlings?

Across the world, there are two types of water; hard water and soft water. Hard water has high levels of calcium and magnesium. Calcium deposits can cause problems to cannabis roots as they can build up in the soil and prevent the absorption of other essential nutrients, thus leading to eventual nutrient deficiencies. Soft water has no mineral deposits whatsoever. Rainwater is technically soft water, but by the time it filters to the plants’ roots through the soil, it is usually filled with useful minerals.
Rainwater is the ideal water for cannabis seedlings, but if accessing rainwater is problematic and you live in an area with hard water, you could try distilled, ionised or purified water.

Do cannabis seedlings need nutrients?

No, seedlings do not need extra nutrients. When they have used all the extra energy supplied by the sucker leaves and seed husk, they will require nutrients from an outside source, but not until they have acquired three to four sets of true leaves and are well on their way in the vegetative phase. The best time to give plants their first dose of fertiliser is when you transplant them to larger containers – day one of the vegetative phase.

Lighting requirements for weed seedlings

It is perfectly possible to use window light to germinate cannabis seedlings, which is certainly the cheapest option. A sunny window sill is fine for the first few weeks after they have germinated. After a couple of weeks, however, it would be best to get a proper LED grow light so you can regulate the light cycles at 18:6 or 24hrs. Seedlings can be grown under fluorescent lighting such as spiral compact fluorescents, tube fluorescents, LEDs or Metal Halides which supply a blue light, which plants use to point towards the light source (phototropism). Avoid incandescent lights as these emit too much heat and insufficient light, and can easily damage delicate seedlings.

LEDs are ideal as they emit hardly any heat. If you use a light source with a high wattage, make sure it is not placed too close to your plants.

Tips for caring for your cannabis seedlings

  • If you want to be a successful cannabis grower, it is important to establish a watering and lighting schedule from the outset and to get into the habit of regularly checking on your plants.
  • Use reflectors or grow tents to maximise the distribution of light.
  • A slight breeze will encourage your shoots to become strong and more likely to grow into healthy, resistant plants. This is because the shoots are forced to focus their energies on reinforcement, rather than simply growing upwards. Try and mimic natural conditions as much as possible, and seedlings in the wild would certainly be subject to gentle breezes.
  • Look out for indications of stalking fungi. Pythium and Rhizoctonia are extremely common parasitic fungi that cause young seedlings to develop a disease known as ‘Damping off’ that results in the plants withering and dying. You can reduce the risk of Damping off affecting your seedlings by always using good sanitation methods, ensuring that the soil is well-drained, and never re-using compost or any other growing medium.

Continue reading: Your guide to the Cannabis Vegetative Stage